Research May 1, 1980 - January 1, 1981. During this period we have progressed in two areas of this project. 1. We have completed the isolation of recombinant DNA molecules containing the transcribed region of the rRNA gene from T. pyriformis. A fragment of the rDNA from a Kpn I site at 3% to the Bc1 I site at 74% on the physical map was cloned in pEN 37, a derivitive of pBR322 which contains an insert of bacterial DNA between the Hind III and Bam H1 sites in pBR322. The Bam and Pvu II sites mapped with restriction endonucleases, and a subclone, pEN 19-1 was isolated which contains from 3% to 16.9% on the physical map of the rDNA. pEN 19-1 contains the transcription initiation site for this gene. The promotor region was mapped by S1 nuclease digestion and the DNA sequence of about 1100 base pairs around the promotor was determined. 2. The transcription termination site was located in pEN 121, a plasmid which contains from 71.6% to 93% on the physical map. The precise locations of the 3' ends of the 35s rRN were determined by S1 nuclease mapping and 450 base pairs of DNA in this region was sequenced.